Microbial communities are key drivers of biogeochemical cycles and several
important industrial processes rely on complex, undefined microbial ecosystems for
production or conversion of substrates for example in wastewater treatment or
anaerobic digestion plants. Despite their significance, such communities are often
poorly defined, if at all. This project concerned previously undefined secondary
microbial communities (SMCs) from photobioreactors culturing cyanobacterium
Arthrospira platensis, known for producing high-value protein-pigment complex C-phycocyanin
(C-PC). C-PC has a range of applications in the
biochemical/pharmaceutical and food industries. Next-generation sequencing
methods were applied to characterize the SMCs sampled over the course of various
batch runs. The bioreactor exerted a strong selective pressure on the SMC, initially
diverse and dynamic, succeeded by a stable and predictable SMC dominated by a
few species. SMC stability and diversity correlated with reactor performance,
especially proliferation and instability of the rare-abundance sub-population;
dominant species ratios were likely less important. The substantially larger
(compared to other species present) A. platensis filaments may represent a dynamic
microenvironment in itself, and if so, constitutes a significant parameter when
optimizing culture conditions. Denser and carefully pre-acclimated inocula reduce
the ecological space available to undesirable taxa (e.g. pathogens) otherwise below
detectable/significant limits. This has implications for other processes that rely on
mixed cultures and may be a control strategy in manufacturing active pharmaceutical
ingredients to cGMP standards. Molecular data was used to obtain several pure
isolates which were characterized further. Strategies to optimize performance with
respect to SMCs were explored and evaluated.
A significant aspect of this CASE project was an industrial placement with Scottish
Bioenergy. The placement involved set-up of a production facility and incremental
scale-up of cultivation from 2 L to 1000 L reactors; development of a downstream
processing protocol covering harvesting, pigment extraction and protein purification,
and some formulation/stability testing. A very low-cost method is described for
obtaining relatively high-purities of C-PC, broadly considered the most costly part of
the entire production process.